In addition to controlling termites, boric acid can be used to control cockroaches and ants. The following “recipes” from a file in our library might be helpful to some of you. Note that any recipe containing boric acid is poison and should be kept out of reach of children, infants and pets.
Mix 1 level teaspoon (5 ml) of boric acid and 2 ½ fluid ounces (75 ml) of corn syrup or honey over heat until the boric acid dissolves. Dilute the bait with an equal volume of water and mix thoroughly. Place two drops of the bait on a strip of white paper and put it where you tend to see ants. Keep the bait moist by adding water or by replenishing the bait (ants seek both moisture and sugar). Borax washing powder can be used instead of boric acid. The bait takes a few weeks to work, so don’t give up if you don’t see an immediate reduction in the number of ants.
Cream ¼ cup (60 ml) of shortening (or bacon drippings) and 1/8 cup (30 ml) of sugar. Mix 8 oz (240 ml or 1 cup) of powdered boric acid (or borax), ½ cup (120 ml) of flour, and ½ of a chopped small onion. Add to the sugar and shortening mixture. Blend well, then add water to form a soft dough. Shape the mixture into small balls. Replace them when they are brick hard. If you keep them in open plastic sandwich bags when baiting, they will stay soft longer. Another recipe included slightly different proportions and/or ingredients: 16 oz (2 cups) boric acid, 1 cup (240 ml) flour, ¼ cup (60 ml) sugar, 1 onion (shortening or bacon drippings omitted).
An article in the Journal of Economic Entomology (volume 90, number 2, pp. 488-491) described an experiment testing the effectiveness of boric acid in killing fire ant colonies (Solenopsis invicta).
Boric acid was dissolved in a sugar bait (10 g of sugar per 100 ml of water) to make solutions of 0.25%, 0.50%, 0.75% and 1.00% (wt:vol).
After six weeks, all of the colonies that were given boric acid were reduced in size (i.e. in number of workers and in amount of brood) by more than 90%. By the sixteenth week, there was a 99% reduction in the number of workers, no brood was present, and any queens that were still alive were small and were no longer producing eggs. The control colonies, on the other hand, grew in size throughout the course of the experiment.
Although the high doses of boric acid currently used in baits are designed to eliminate ants quickly, the authors point out that a high dose increases the likelihood that ants will learn to avoid the bait. Because a high dose kills ants quickly, it also reduces the passing of food from one ant to another (which could ensure that many more ants encounter the poison).
The concentrations of boric acid used in this experiment are much less than the concentration that is currently being used or recommended in ant baits. The authors concluded, “We suggest that if it is used at lower concentrations, boric acid has great potential for control of S. invicta.”